FAQ

What kinds of galaxies is ELLIPROF for? Smooth light distributions: elliptical and lenticular galaxies, bulges, and other early-type systems. It describes a galaxy as nested ellipses, so it is not the right tool for irregular galaxies or strongly structured light (spiral arms, bars, bright clumps).

Does elliprof find the galaxy centre? No. You give the initial centre (X0, Y0). ELLIPROF then fits a centre for every isophote.

Does elliprof estimate the sky? No. Give it with --sky or --sky-image.

Does elliprof make masks? No. It uses a mask you make. See Sky and masks.

Why is my first isophote unchanged, with I3 = I4 = 0? It had too few usable samples (for example, it lies inside a masked nucleus), so it kept its starting values. elliprof prints a note. Start at a larger R0.

What units is I0 in? The image's units per pixel, after the sky is subtracted. See Galaxy surface photometry to convert to mag/arcsec².

Are there uncertainties on the profile? No. Estimate them from repeated fits with different skies, masks or starting values, or from simulations.

Why does alpha jump from ~2° to ~178°? It is an axis direction, 0–180°, so 2° and 178° are only 4° apart. Unwrap it before plotting (see The profile).

Is A4 = 0 the same as A4 = 90? Yes. Both mean extra light along the axes: disky.

Do --model-harmonics and COS3X/COS4X change the fit? No, only the model image (and so the residual). The exception is --sixth-order (COS3X < 0), which changes the fit.

Can I get the profile as an image? The profile is a table. The model image (-m) is the profile turned into an image. Plot the profile from the CSV or with read_profile.

Does the model have the WCS of my image? Yes. The model, residual and prepared images carry the header of the science HDU, WCS included.

Can I fit an image in a FITS extension? Yes: 'galaxy.fits[SCI]' or 'galaxy.fits[1]', quoted.

Can elliprof measure SBF distances? No. It provides the model and residual an SBF analysis starts from. See ELLIPROF's role in SBF.

How is elliprof related to the original ELLIPROF? The fitting code is the original ELLIPROF, compiled unchanged. See How elliprof is built.

How should I cite it? Cite the software with its version and repository (https://github.com/ekourkchi/elliprof). State that ELLIPROF was originally developed by John Tonry as part of MONSTA. Report the parameters you used.

Where do I report a problem? https://github.com/ekourkchi/elliprof/issues. Include the output of elliprof --diagnostics.